The international ratings agency S&P has revised its ratings outlook for a host of Chinese companies. The firms are predominantly state-owned mega  corporations in China's banking, electricity and energy sectors.

Companies involved include big names like the China National Petroleum Corp., China Development Bank and Bank of Communications. The ratings for  the companies were maintained but their outlooks were revised from stable to negative.

On Thursday, S&P made the same decision for China's sovereign credit rating outlook, revising it to negative from stable, but maintained the rating  at AA-. S&P said the government's reform agenda is on track but likely to proceed more slowly than expected.